1. Field of the Invention
This invention relates to an automatic shift-down apparatus for an automatic transmission which comprises vehicle speed detection means for detecting the speed of a vehicle; vehicle-speed variation rate calculation means for calculating the variation rate of the detected vehicle speed; shift-start vehicle speed calculation means for calculating, on the basis of the calculated vehicle-speed variation rate and a time required to complete a shift operation, a shift-start vehicle speed which enables the shift operation to finish before the vehicle speed attains a shift-completion speed; and a shift device which starts a shift operation when the detected vehicle speed attains the calculated shift-start vehicle speed.
2. Description of the Prior Art
In a conventional electronic-control automatic transmission which utilizes a manual transmission and which is operated by means of hydraulic pressure or a motor, when a driver decelerates or stops the vehicle while maintaining a certain shift position, the transmission must be automatically shifted down to a certain lower gear before the vehicle stops, in order to enable smooth resumption of travel.
The above-described conventional electronic-control automatic transmission has the following drawback. Since gear changes are performed in a constant manner, in some cases, the vehicle cannot resume travel smoothly, because the deceleration of the vehicle varies depending on the driver and surrounding conditions.
It is a general object of the present invention to provide an automatic shift-down apparatus for an automatic transmission which enables changeover of the operation time (or the speed) of an automatic shift-down operation depending on the variation rate of vehicle speed and to enable the automatic shift-down operation to be performed at an optimal timing which is determined on the basis of driving conditions, to thereby improve the drive feeling.
It is a more specific object of the present invention to provide an automatic shift-down apparatus and method for an automatic transmission in which the variation rate of a detected vehicle speed is calculated; on the basis of the calculated variation rate of vehicle speed and a time required to complete a shift operation, there is calculated a shift-start vehicle speed which enables the shift operation to finish before the vehicle speed attains a shift-completion speed; and when the detected vehicle speed attains the calculated shift-start vehicle speed, the shift operation is started.
It is another object of the present invention to provide an automatic shift-down apparatus for an automatic transmission characterized by comprising: vehicle speed detection means for detecting the speed of a vehicle; vehicle-speed variation rate calculation means for calculating the variation rate of the detected vehicle speed; shift-start vehicle speed calculation means for calculating, on the basis of the calculated vehicle-speed variation rate and a time required to complete a shift operation, a shift-start vehicle speed which enables the shift operation to finish before the vehicle speed attains a shift-completion speed; and a shift device which starts a shift operation when the detected vehicle speed attains the calculated shift-start vehicle speed.
It is still another object of the present invention to provide an automatic shift-down apparatus for an automatic transmission characterized by further comprising first vehicle-speed variation rate calculation means for calculating the first variation rate of vehicle speed when the detected vehicle speed has attained the calculated shift-start vehicle speed.
It is a further object of the present invention to provide an automatic shift-down apparatus for an automatic transmission characterized by further comprising vehicle-speed variation rate storage means for storing the calculated vehicle-speed variation rate of the vehicle speed when the detected vehicle speed has attained the calculated shift-start vehicle speed.
It is a still further object of the present invention to provide an automatic shift-down apparatus for an automatic transmission characterized by further comprising second vehicle-speed variation rate calculation means for calculating the second variation rate of vehicle speed after the detected vehicle speed has attained the calculated shift-start vehicle speed.
It is a yet further object of the present invention to provide an automatic shift-down apparatus for an automatic transmission characterized by further comprising comparison means for comparing the second calculated vehicle-speed variation rate after the detected vehicle speed has attained the calculated shift-start vehicle speed with the first calculated vehicle-speed variation rate stored in the vehicle-speed variation rate storage means.
It is a yet further object of the present invention to provide an automatic shift-down apparatus for an automatic transmission further comprising shift speed control means for controlling the speed of the shift operation in accordance with the result of comparison performed by the comparison means which indicates whether the second vehicle-speed variation rate after attainment of the shift-start vehicle speed is greater or less than the first vehicle-speed variation rate at the time of attainment of the shift-start vehicle speed.
It is another object of the present invention to provide an automatic shift-down apparatus for an automatic transmission characterized in that when the calculated vehicle-speed variation rate indicates that the vehicle comes into an accelerating state after the initiation of the shift operation, the transmission is shifted to a gear in response to the vehicle speed.
It is a further object of the present invention to provide an automatic shift-down method for an automatic transmission comprising: calculating the variation rate of a detected vehicle speed; calculating a shift-start vehicle speed which enables the shift operation to finish before the vehicle speed attains a shift-completion speed, on the basis of the calculated vehicle-speed variation rate and a time required to complete a shift operation; and starting a shift operation when the detected vehicle speed attains the calculated shift-start vehicle speed.
In the automatic shift-down apparatus for an automatic transmission according to the present invention, the vehicle speed detection means detects the speed of a vehicle; the vehicle-speed variation rate calculation means calculates the variation rate of the detected vehicle speed; the shift-start vehicle speed calculation means calculates, on the basis of the calculated vehicle-speed variation rate and a time required to complete a shift operation, a shift-start vehicle speed which enables the shift operation to finish before the vehicle speed attains a shift-completion speed; and the shift device starts a shift operation when the detected vehicle speed attains the calculated shift-start vehicle speed.
Therefore, the automatic shift-down apparatus for an automatic transmission according to the present invention has an advantage such that the operation time (or the speed) of the automatic shift-down operation can be switched depending on the variation rate of vehicle speed.
In the automatic shift-down apparatus for an automatic transmission according to the present invention, the first vehicle-speed variation rate calculation means calculates the variation rate of vehicle speed when the detected vehicle speed has attained the calculated shift-start vehicle speed.
Therefore, the automatic shift-down apparatus for an automatic transmission according to the present invention has an advantage such that the shift control can be performed on the basis of the variation rate of vehicle speed when the detected vehicle speed has attained the shift-start vehicle speed.
In the automatic shift-down apparatus for an automatic transmission according to the present invention, the vehicle-speed variation rate storage means stores the calculated vehicle-speed variation rate of the vehicle speed when the detected vehicle speed has attained the calculated shift-start vehicle speed.
Therefore, the automatic shift-down apparatus for an automatic transmission according to the present invention has an advantage such that the stored vehicle-speed variation rate of the vehicle speed, when the detected vehicle speed has attained the shift-start vehicle speed, can be used after attainment of the shift-start vehicle speed.
In the automatic shift-down apparatus for an automatic transmission according to the present invention, the second vehicle-speed variation rate calculation means calculates the second variation rate of vehicle speed after the detected vehicle speed has attained the calculated shift-start vehicle speed.
Therefore, the automatic shift-down apparatus for an automatic transmission according to the present invention has an advantage such that the shift control can be performed on the basis of the variation rate of vehicle speed after the vehicle speed has attained the shift-start vehicle speed.
In the automatic shift-down apparatus for an automatic transmission according to the present invention, the comparison means compares the second calculated vehicle-speed variation rate after the detected vehicle speed has attained the calculated shift-start vehicle speed with the first calculated vehicle-speed variation rate stored in the vehicle-speed variation rate storage means.
Therefore, the automatic shift-down apparatus for an automatic transmission according to the present invention has an advantage such that the shift control can be performed on the basis of the result of comparison.
In the automatic shift-down apparatus for an automatic transmission according to the present invention, the shift speed control means controls the speed of the shift operation in accordance with the result of comparison performed by the comparison means which indicates whether the second vehicle-speed variation rate after attainment of the shift-start vehicle speed is greater or less than the first vehicle-speed variation rate at the time of attainment of the shift-start vehicle speed.
Therefore, the automatic shift-down apparatus for an automatic transmission according to the present invention has an advantage such that the automatic shift-down operation can be performed at an optimal timing which is determined on the basis of driving conditions, to thereby improve drive feeling.
In the automatic shift-down apparatus for an automatic transmission according to the present invention, when the calculated vehicle-speed variation rate indicates that the vehicle comes into an accelerating state after the initiation of the shift operation, the transmission is shifted to a gear in response to the vehicle speed.
Therefore, the automatic shift-down apparatus for an automatic transmission according to the present invention has an advantage such that the gear shift can be performed in consideration of variations in conditions.
In the automatic shift-down method for an automatic transmission according to the present invention, the variation rate of a detected vehicle speed is calculated; on the basis of the calculated vehicle-speed variation rate and a time required to complete a shift operation, a shift-start vehicle speed is calculated such that the shift operation can finish before the vehicle speed attains a shift-completion speed; and a shift operation is started when the detected vehicle speed attains the calculated shift-start vehicle speed.
Therefore, the automatic shift-down method according to the present invention has an advantage such that the operation time (or the speed) of the automatic shift-down operation can be switched depending on the variation rate of vehicle speed.